Templates: Fix "Discard changes?" dialog after creating template with master template (fixes #20262) (#20749)

Moves the _data.updateCurrent() call inside the updateLayoutBlock conditional
in setMasterTemplate(). This prevents spurious change detection when loading
templates from the server, while maintaining proper change tracking when users
actually modify the master template via the UI.

This completes the fix started in PR #20529 which added the updateLayoutBlock
parameter but inadvertently left the data model update outside the conditional.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

src/Umbraco.Web.UI.Client/src/packages/templating/templates/workspace/template-workspace.context.ts

@@ -123,9 +123,8 @@ export class UmbTemplateWorkspaceContext
 
 		if (updateLayoutBlock) {
 			this.#updateMasterTemplateLayoutBlock();
-		}
-
 			this._data.updateCurrent({ masterTemplate: unique ? { unique } : null });
+		}
 
 		return unique;
 	}